Oriented strandboard (OSB) is a wood based panel product, the principal component of which is wood strands. The strands are generated by removing the bark from logs and then exposing the logs to an assembly of rotating knives that slice strands from the logs. Because the strands have a high moisture content at this point in the process, they must be dried before they are further processed into the final product. The wet strands are therefore collected and fed into a dryer, after which they are discharged and blended with adhesive. The strands are then oriented by a series of "forming heads" to create a continuous mat of strands. The mat of strands is then separated into discrete lengths which are then compressed and heated to produce panels. The panels are then sawed, sanded, and otherwise processed into the finished product.
The current method of drying strands for OSB production is to feed the wet strands into a rotary dryer. Such dryers tumble the strands while exposing them to a flow of heated air, the inlet temperature of which is typically 800.degree. F. or higher. However, the current method has several disadvantages.
One such disadvantage is the generation and emission of airborne pollutants. Such pollutants include particulate matter entrained in the drying airstream and gaseous pollutants such as carbon monoxide. Although secondary and tertiary cleaning equipment may be used in an attempt to separate particulate and gaseous matter from the airstream prior to its discharge into the atmosphere, such systems are expensive and may still allow a single, typical plant to exhaust hundreds of tons of particulate and gaseous matter into the atmosphere.
Another significant disadvantage of current methods is strand breakage, which occurs due to the tumbling action of the dryer drum, the impact of strands with internal components of the dryer, and the action of rotating airlocks at the dryer infeed and discharge. The broken strands may be either screened out of the process flow or incorporated into the final product. However, if the strands are incorporated into the final product, the quality of the finished board is degraded. Given that a significant quantity of strands processed under current methods break, strand breakage results in a considerable loss industry-wide.
A need therefore exists for a method for drying strands or other similar wood products wherein the occurrence of strand breakage is reduced and the emission of airborne pollutants is reduced.